There are in the prior art various wireless communications devices for establishing an ad hoc communications network providing on-site communication for companies or organizations that have mobile users in need of instant communications for purposes of sharing information, coordination activities, and supervision or management of employees. The distance over which they need to communicate is generally limited to a site, facility, campus, building, premises or other local geographical area.
The geographic extent of these prior art communications systems are however limited by the transmit power and effective range of the individual user devices themselves. In the unlicensed 902-928 MHz bands used for industrial, scientific, and medial (ISM) applications, for example, devices with a transmit power of 100 milliwatts may have a maximum transmit range of 500 feet, and less where natural and man-made obstructions attenuate and or reflect transmissions. Users located more than 500 feet away are generally unable to communicate and must rely on one or more dedicated repeaters or other type of network infrastructure to extend the effective range of the network. Such infrastructure is, however, expensive to install and maintain, results in fixed black-out zones depending on local terrain and structures, and virtually useless when a user device and repeater are out of range of one another.
There is therefore a need for a flexible communication system that enables users to place and receive calls between users who may be out of transmit range of one another without the need for repeaters or other infrastructure being located every location the users may be located or location to which the users may migrate. The system should also be able to deploy and administer itself with little or no external control or guidance while being flexible enough to cope with changing network conditions—connecting mobile nodes new to the network, disconnecting mobile nodes that depart from the network, and routing around occasion link failures between individual pairs of nodes—while still maintaining communications between the various nodes.